This invention generally relates to improvements in a process for manufacturing pneumatic tires and in tires manufactured in accordance therewith. More particularly, this invention is concerned with (a) improvements in a process for manufacturing pneumatic, radial-ply tires, wherein each of the tires includes an improved pair of oppositely disposed beads and a ply extending therebetween and looped about the respective beads; and (b) tires manufactured in accordance with the improved process.
The art of manufacturing a pneumatic tire has evolved over the years to include a number of widely used variations of a conventional process which includes the basic steps of: (a) selecting a plurality of raw materials, including chemicals, different kinds of rubber, woven elastomeric fabrics for plies, puncture resistant woven belts and steel wire for tire beads; (b) mixing the selected rubbers with various processing oils, carbon black, pigments, antioxidants, accelerators and other additives, to form different rubber compounds; (c) processing, rolling and cutting the rubber compounds for use in forming the innerliner, sidewalls, tread and other rubber components of the tire; (d) assembling the rubber components, plies, belts and beads together on the drum of a tire building machine, and, under heat and pressure, forming therefrom a xe2x80x9cgreenxe2x80x9d tire; (e) inserting the green tire into a vulcanizing mold; and (f) curing the green tire by expanding a bladder therewithin, through the introduction into the bladder of a high pressure medium at a sufficiently elevated temperature to vulcanize the green tire and to conform the tire to its final design shape, including the tire tread pattern and sidewall markings.
Despite numerous attempts to optimize the above described conventional manufacturing process, tires manufactured in accordance prior art processes continue to exhibit non-uniformities in their shape and other deficiencies in their physical characteristics, to which uneven tire wear is generally attributable. For example, it is not unusual to observe that when a prior art tire is mounted on a rim and inflated, the inner, radially-extending, heel seats of the opposed bead portions of the tire are not disposed in abutment with the outer, radially-extending, flange shoulders of the wheel rim, with the result that unbalanced forces are outwardly radially transmitted to the tire tread, causing the tread to become unevenly worn. In addition, due to unrelieved internal stresses developing in prior art tires, in the course of their manufacture, internal flow cracks have been observed to develop in one or the other of the opposed tread shoulders, causing the tires to become unevenly worn.
Of course, processes of manufacturing tires having various structural forms have been the subject of numerous prior art patents. For example: U.S. Pat. No. 3,900,061; U.S. Pat. No. 4,669,519; and U.S. Pat. No. 4,867,218 are directed to subject matter such as improvements in tire cornering performance, the reduction in tire rolling resistance, and the avoidance of the need for larger tire curing presses. In addition, U.S. Pat. No. 4,393,912, issued to Gouttebessis discloses a process of molding a pneumatic tire comprising a crown and opposed sidewalls, wherein each of the sidewalls is terminated by an unreinforced bead, wherein the tire is molded from liquid or paste materials which solidify between an outer mold and an inner core, and wherein the opposed beads are located axially outwardly of their mounted position on a wheel rim. Since the beads are so located, it is necessary to press the opposed bead portions axially toward one another when mounting the tire on the wheel rim.
Despite such steady improvements in tire construction and their manufacturing processes, as described by the prior art, there still exists a need for modifications of the conventional tire manufacturing processes to focus on relieving internal stresses that develop in tires in the course of their manufacture and on avoiding imparting internal stresses to tires in the course of mounting them on wheel rims. In this connection, it has been found that a major factor contributing to the build-up of stresses in prior art tires, is that the ply and rubber around the beads in the opposed bead portions of the tires have a tendency to twist the beads in the course of manufacture of the tires, generally due to the opposed bead portions being required to be moved toward one another in the course of manufacture of the tires. Such internal stresses tend to cause physical deformities and other physical deficiencies to develop in the resulting tires, causing the tire treads to become unevenly worn when in use. Moreover, internal stresses leading to uneven tread wear are developed in tires when the opposed bead portions of the tires are required to be moved toward one another to mount the tires on wheel rims.
A preferred embodiment of the present invention includes a pneumatic tire having a tread, and a carcass with a ply, oppositely disposed sidewalls extending radially-inwardly from opposite sides of tread and including an inner radial-end bead portion with an annulus made of bead wire and with the ply extending between and looped about each of the beads. Each of the beads includes an annulus made of a rubber filler forming a bead member with the bead wire annulus associated therewith. The bead member has a substantially circular transverse cross-section. Each of the beads includes a thermoplastic cover disposed in surrounding relationship the bead member thereof. Each of the thermoplastic covers includes an inner layer and an intermediate layer and an outer layer. The inner and outer layers of the thermoplastic cover are selected from a class of materials, e.g., a polymer plastic fabric, that soften at a lower temperature than the intermediate layer, e.g. a polyethylene film. Moreover, the inner and outer layers can be of one or more turns of a square-woven nylon fabric coated on both sides with an adhesive.
It is also within the terms of the present invention to provide a bead member for a pneumatic tire including a bead wire annulus and a thermoplastic cover disposed in surrounding relationship therewith. The bead includes a rubber filler annulus which, with the bead wire annulus, forms a bead member having a substantially circular transverse cross-section. The thermoplastic cover is characterized by an inner layer, an intermediate layer and an outer layer. The inner and outer layers of the thermoplastic cover are selected from a class of materials, e.g., a polymer plastic fabric, that soften at a lower temperature than the intermediate layer, e.g. a polyethylene film. Moreover, the inner and outer layers can be of one or more turns of a square-woven nylon fabric coated on both sides with an adhesive.